Saturable reactor control circuit



K. L. SHRIDER ETAL SATURABLE REACTOR -CONTROL CIRCUIT tmb tm 2Go Oct. 8, 1957 United States Patent() SATURABLE REACTOR CONTROL CIRCUIT Kenneth L. Slirider and Robert W. Pfaff, Cleveland, Ohio, assignors to The Reliance Electric & Engineering ComL pany, a corporation of Ohio Application August 4, 1953, Serial No. 372,236

9 Claims. (Cl. 32a-89)' The invention relates in general to circuits containing anunwanted voltage source, in which it is desired to obtain a current ow independent of this unwanted voltage source. ln particular, it relates to circuits containing an inductive impedance in which the induced voltage due to self-inductance is the unwanted voltage source, and to circuits containing an inductive impedance into which an alternating voltage induced due to the action of other circuits represents the unwanted voltage source; and in which a current flow independent of these unwanted voltage sources is desired. More particularly, it relates to circuits in which the current ow is controlled by the action of a pentode tube or other device having constant current passing characteristics so that the current iiow is determined by the action of the pentode tube or other said device and is not affected by the action of the unwanted voltage source. winding of asaturable reactor.

Saturable reactors generally have a closed magnetic circuit with a middle leg, a direct current control winding on the middle leg, and separateralternating current windings on the two outer legs. Variations inthe amount of current supplied to the control windingvariably saturate the saturable core whichcauses inverse'variations in the inductive reactance of the alternating current windings. The4 odd harmonics of the alternating current supply voltage cancel out in the middle leg; however, the even harmonics are present with the second harmonic being predominant. This second harmonic voltage can be quite large and damaging since -a second harmonic current could flow in this control winding because of the second harmonic voltage. method of supplying current to the'control winding, commonly termed a direct current winding', of a saturable reactor orother winding having an induced voltage thereinfwherein the control tubehas a constant current passing characteristic, and as such, any variations of anode-cathode voltage on the-control tubewill notaflect an anodecathode' current, and hence, willv not cause any variations in current in the control winding. Similarly, any load impedance serially'connected with; the control winding will have'a substantially lpure voltage'developed thereacross' which is free of all alternating voltages such as'would otherwise be caused by the second harmonic voltage on the control winding.

An object of'theinvention' is to provide-'asubstantially pure voltage proportional to a controlv inputgridl signal voltageirrespective ofA unwanted alternating voltages present in the circuit.

Another object ofthe'invention is toprovidea control circuitffor a saturablcreactor ina phase shift control of a power converter wherein the saturationofthe corefof the saturable reactor depends only upon the `control volt# age input to a control tube in series withthe saturable reactor control winding andnot upon any alternating current' caused by alternating yvoltages induced intothe saturable 'reactor control winding.

Another'V objecfofthe invention is to use a constant This current may be passed `to a, control Thepr'esent' invention relates to a` current conducting device in series with a saturable reactor control winding.

Another object of the invention is to provide a saturable reactor control circuit which is immune to the effects of any alternating voltages in the control winding of the saturable reactor.

Another object of the invention is to provide a control circuit wherein the flux change in an inductive winding may be rapidly effected.

Another object of the invention is to provide a voltage controlled by the signal and not containing alternating current from an unwanted alternating current signal also present. This voltage may be used for antihunt, and may also be used for other purposes.

Another object of the invention is to provide a control tube in series with a control winding of a saturable reactor which circuit includes an antithunt device which is thereby rendered immune to any alternating voltage in the saturable reactor control winding.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

Figure l is a schematic diagram of a control circuit for controlling the power converter; and

Figure 2 is a diagrammatic view of a saturable reactor used in the circuit of Figure l.

The Figure l shows a schematic diagram wherein a power converter 11 supplies electrical energy to a load 12. Feedback connections 13 lead from the load 12 -to a grid bias supply 14 which in turn supplies Variable grid bias to a control tube 15 in series with a saturable reactor control winding 16. The control winding 16 is shown in Figure 2 as being wound on the middle leg 17 of a saturable reactor core 18. The core 18 is part of a saturable reactor 19 also including alternating current windings 20 and 21 wound on outer legs 22 and 23 thereof. The two alternating current windings 20 and 21 are shown in Figure l-as part of a phase shifting network 26. The phase shifting network 26 may be supplied with operating alternating current voltage by any suitable means such as the transformer 25. The alternating current windings 20 and 21 are in series with a condenser 27 in this phase shifting network 26, and such network may be similar to that shown in Patent No. 2,524,759, issued October l0, 1950, entitled Phase Shift Network. The network 26 is connected to control the converter 11, and such converter may be rectifier tubes having` a variable output depending upon the phase of the grid voltage with respect to a supply voltage source so that a variable direct current output may be supplied to the load 12.

A direct current power supply 28 supplies the operating voltage for the amplifier 15. This amplier has been shown as a high vacuum pentode 31 having an anode 32, cathode 33, control grid 34, screen grid 35, and suppressor grid 36. The direct current control winding 16 has terminals 37 and 38. The terminal 37 is connected to the anode 32, and the terminal 38 is connected through a resistor 39 to a positive direct current terminal 4i). The voltage at the terminal 40 is obtained from the power supply 28. This power supply may be generally conventional having a supply transformer 41 feeding bridge rectifier 42,V with the output of this rectifier iiltered by the choke 43 and condensers 44 and 45. Filtered direct current appears at the positive terminal 46, and this voltage' is utilized as an operating voltage in the converter 11 and connected thereto by a lead 47. Ground lead 51 is also connected to the converter 11 by a lead 61 as a return circuit. Another stage of filtering represented by a choke 48 and condenser 49iis used to obtain a purer direct current at the-terminal 40. The screen grid 35 is connected by` a lead 50 to this .terminal 40. A lead 51 connects to E the bridge rectifier 42 and to the grid bias supply 14. An optional resistor 52 may be used to connect the cathode 33 to the lead 51. The use of the resistor 52 is optional to reduce the gain of the circuit when desired. It also makes the circuit more immune to the efects of the second harmonic voltage.

An antihunt circuit 53 includes a condenser 54 and resistor 55 connected in series between the terminal 38 and the control grid 34. A bias lead 56 connects the control grid 34 and the grid bias supply 14. A loading resistor 57 may be connected across the direct current control winding lo, if the induced alternating voltage in the control winding 16 exceeds the constant current region of the pentode or other device 3i..

Operation The circuit is designed to prevent any alternating volt age existing or induced in the control winding lo from ini'luencing the current through that winding, such current in the winding being controlled only by the control voltage, in this case the output of grid bias supply 3.4. The amplifier or control tube i5 has been shown as being a high vacuum pentode 3l which has a characteristic such that throughout a portion of its operating range any variations in the anode-cathode voltage have substantity 'ly no eli-lect on the anode-cathode current. This means that it is essentially a contant current passing device. Pentodes have a substantially flat curve of the graph ot plate current versus plate voltage as long as a certain minimum plate voltage is maintained. ln the normal operating range the direct current plate supply to the pentode will be suicient to maintain the operation of the pentode in this constant current region. The anode current is dependent on the screen voltage; and hence, the screen supply has been connected to terminal 40 which is a well filtered direct current source, and has an additional L section iilter itl-49 after the positive terminal which supplies other direct current loads, such as a control section in the converter 11. Tetrodes, beam power tubes, and transistors are examples of other substantially constant current passing devices which may be utilized in many circumstances in this circuit.

The Figure 2 shows the construction of a typical saturable reactor wherein the direct current control winding 16 is on the middle leg i7 and with the two alternating current windings 2l) and 2l on the outer legs. Arrows 58 show the unidirectional nature of the ux caused by the control winding 16 whereas arrow 59 indicates the tlux instantaneously established by alternating current winding Ztl, and arrow 66 indicates the instantaneous flux established by alternating current winding 21. It will be noted that at a given instant the fluxes 58 and 59 in the leg Z?. are additive whereas the uxes 58 and 6i) in the leg 23 are subtractive. This means that the two legs 22 and 23 are operating on different portions of the hysteresis curve. The net eect is that the fundamental and odd harmonics of the supply frequency cancel out in the middle leg 17; however, even harmonics are present therein. This means that even harmonics o flux with the second harmonic predominating will establish even harmonics of voltage in the direct current con trol winding in the normal case these may be from thirty to titty volts R. M. S. for an alternating current supply voltage of eighty volts for example on the two alternating current windings 20 and 2l. In many aggravated conditions, however, depending upon the type ot load and the turns ratio between alternating current and direct current windings, the second harmonic voltage may as high as three hundred volts for the same alternating current input voltage. IE the amplifier 15 were an amplier that responded to these alternating current voltages, then an alternating current at the second harmonic frequency would liow through the direct current control winding lo. This in turn would establish second harmonic voltages in the alternating current windings 20 and 21 of very high value which would impair the proper operation of the phase shifting network 26.

The present invention utilizes a control tube l5 which is an essentially constant current device so that variations of alternating current supply voltage will have no effect on the current passed by the amplifier l5 to the control winding i6. Further, the voltage developed across resistor 39 will be inuenced only by the variable grid bias supplied by grid bias supply irl, and this voltage may be used for control purposes. The loading resistor 57 is used to load the direct current control winding lo so as to reduce the second harmonic voltage appearing thereacross so that the alternating voltage in the control winding does not exceed the constant current region of the pento-de or other device.

The essentially pure direct current voltage appearing across the load resistor 39 is obtained without filtering even though the relatively high alternating voltage due to the control winding liti is present in the same series circuit. The terminal {it} will be maintained at a substantially constant positive direct current value. The terminal 38 will be maintained at a voltage which is constant for each individual operating condition, in turn dependent upon the amount of grid bias supplied to the amplifier l5. The terminal 37 will swing up and down with the alternating current voltage induced in the control winding lo. However, this voltage variation will be equal and opposite across the control winding 16 and amplilier l5 so that no alternating current voltage variation appears upon terminal 3S.

The voltage developed across the load resistor 39 may be utilized in any desired manner, and the instant circuit utilizes this voltage in the antihunt circuit 53. This antihunt circuit may or may not include the resistor 55, the presence of such resistor serving to phase properly the antihunting signal with respect to the signal from grid bias supply 14. Hence, it has been shown as a variable resistor. The grid bias supply may be assumed to supply a negative bias on the grid 34 relative to the cathode 33. The feedback connections 13 from the load l2 to the bias supply i4 may dictate some change in grid bias; for example, such change may be positive, or less negative, on the grid 3:4. This will tend to malte the amplier 15 pass more current. This will create a greater voltage drop on the load resistor 39, making the terminal 33 less positive. The total voltage charge on the condenser 54 will tend to remain momentarily the same and thus will tend to drive the control grid 34 more negative. This is the opposite of that control dictated by the grid bias supply 14, and hence, is an antihunt circuit. Since the condenser 54 is counected to the terminal 38 and is responsive to the voltage across the resistor 39, the antihunt circuit has an effectiveness depending upon the amplification factor of the control tube 15. This makes a very powerful and effective antihunt circuit.

(The resistor 52, besides reducing the gain of the circuit, may serve an additional function. Any small residual alternating current through the control tube 31 will cause an alternating voltage to appear across the resistor 52. This has a degenerative ellect on the grid to cathode voltage to further reduce the alternating current through the control tube. The voltage across resistor 52, or resistor 39, may be used for antihunt or other control purposes.

The control winding 16 is one example of an inductive winding which may have an alternating voltage induced therein or an example of some series circuit including a direct current operating voltage wherein the series circuit has injected therein an alternating voltage and wherein the circuit is selective to produce a direct current voltage dependent only upon the direct current control input and not dependent upon the alternating voltage.

The .control winding 16 is representative of some form ofinductive impedance, and this inductive winding naturally resists any change in the current therein. To resist this change in current a Avoltage is developed within the inductance, proportional to the rate of change of current, which opposes the change of current. Since the pentode is a substantially constant-current device this voltage will have no effect and the current in the inductive impedance will be changed to its new value extremely rapidly.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been .made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. AV control circuit comprising, an inductive winding, a control tube having cathode, anode, and control grid means, said control tube having a characteristic throughout a portion of its operatingrange such that variations in anode voltage have substantially no affect on the anode current, a voltage source, a load impedance, means for connecting in series said voltage source, load impedance, inductive winding and control tube, said series circuit adapted to have an alternating voltage therein, input means connected to said control grid means and cathode means to control the current passed by said control tube to said inductive winding, whereby the voltage across saidv load impedance is substantially independent of the alternating voltage in said series circuit, and said voltage may be changed rapidly relative to the time constant o the inductive Winding, a utilization circuit, and means for connecting said utilization circuit between the control grid means and the junction of said load impedance and said inductive winding, to thus have substantially no alternating voltage from the alternating voltage in said series circuit appear in said utilization circuit.

2. A control circuit comprising, an inductive Winding adapted to have an alternating voltage thereon, a control tube having cathode, anode, and control grid means, said control tube having a characteristic throughout a portion of its operating range such that variations in anode voltage have substantially no affect on the anode current, a load impedance, a direct current source, means for connecting in series said load impedance, direct current source, inductive winding and control tube, input means connected to said control grid means and cathode means to control the current passed by said control tube to said load impedance, whereby the voltage across said load impedance is substantially independent of the alternating voltage in said inductive winding, a load circuit, and means for connecting said load circuit to said impedance to thus have substantially no alternating voltage from Said inductive winding appear in said load circuit.

3. A control circuit comprising, a permeable core, a winding on said permeable core and adapted to have an alternating voltage thereon, a control tube having cathode, anode, and control grid, said control tube having a characteristic throughout a portion of its operating range such that variations in anode voltage have substantially no affect on the anode current, a direct current source, a load impedance, means to connect in series said direct current source, load impedance, winding and control tube, control voltage input means connected to said control grid and cathode to control the current passed by said control tube to said control winding and impedance, whereby the voltage across said load impedance is substantially independent of the alternating flux in said permeable core, a load circuit, and means for connecting Said load circuit to said impedance to thus have subimpedance, said control winding being connected to saidV anode and to said impedance, said direct current source being connected across the series -combination of said impedance, control winding and said pentode, control voltage input means connected to said control grid andV cathode to control the current passed by said pentode to said impedance, whereby the voltage across said impedance is substantially independent of the alternating ux in said permeable core, a load circuit, and means for connecting said load circuit to said impedance to thus have substantially no alternating voltage from said alter'- nating current winding appear in said load circuit.

5. A control circuit comprising, a phase shifting network having an alternating current reference voltage input and an alternating current output, a saturable reactor having a permeable core and an alternating current winding as a variable inductance in said phase shifting network, a control winding on said permeable core,l a high vacuum pentode having cathode, anode, and control grid, said pentode having a characteristic throughout a portion of its operating range such that variations in anode-cathode voltage have substantially no affect on the anode-cathode current, an operating voltage source, an impedance, an external anode-cathode circuit for said pentode including, means for connecting said impedance and said control winding in series therein and means for operating said pentode from said operating Voltage source, a load circuit, and means for connecting said load circuit to said impedance to thus have substantially no alternating voltage from said alternating current winding appear in said load circuit.

6. A control circuit comprising, a winding adapted to have alternating voltage thereon, a control tube having cathode, anode, and control grid means, an operating voltage source, a load impedance, said winding being connected to said anode, said operating voltage source being connected across the series combination of said winding, load impedance and control tube, said control tube having a characteristic throughout a portion of its operating range such that variations in anode-cathode voltage have substantially no affect on the anode-cathode current whereby the alternating voltage on said Winding will not appear at the terminal thereof remote from said ano-de means, an antihunt circuit including condenser, and means for connecting said antihunt circuit between the control grid means and said remote terminal, to thus have substantially no alternating voltage from the alternating voltage on said winding appear in said antihunt circuit.

7. A control circuit comprising, a phase shifting network having an alternating current reference voltage input and an alternating current output, a saturable reactor having a permeable core and an alternating current winding as a variable inductance in said phase shifting network, a control winding on said permeable core, a pentode tube having a cathode, an anode, and control grid, said pentode tube having a characteristic throughout a portion of its operating range such that variations in anode-cathode voltage have substantially no aiiect on the anode-cathode current, a direct current operating voltage source, a load impedance, said control winding being connected between said anode and said load impedance, said direct current source being connected across the series combination of said load impedance, control winding and said pentode tube with the positive terminal connected to said load impedance, an antihunt circuit including a condenser connected between the control grid and the junction of said load impedance and control winding, control voltage input means connected to said control grid and cathode to control the current passed by said pentode tube to said control winding, whereby the voltage across said load impedance is substantially independent of the alternating linx in said permeable core.

8. A control circuit comprising, a phase shifting network having an alternating current reference voltage input and an alternating current output, a saturable reactor having a permeable core and an alternating current winding as a variable inductance in said phase shifting network, a control winding on said permeable core to variably control the saturation thereof, the variable saturation of said core causing even harmonics of said reference voltage to appear in said control winding, a high vacuum pentode having a cathode, an anode, and screen and control grids, said pento-de having a characteristic throughout a given portion of its operating range such that variations in anode-cathode voltage have substantially no affect on the anode-cathode current, a direct current operating voltage source of a voltage value to operate said pentode in said given portion of its operating range, a load impedance, said control winding being connected between said anode and said load impedance, said direct current source being connected across the series combination of said load impedance, control winding and said pentode with the positive terminal connected to said load impedance, said screen grid being connected to the positive terminal of said direct current source, an

antihunt circuit including a serially connected resistor and condenser connected between the control grid and the junction of said load impedance and control winding, control voltage input means connected to said control grid and cathode to control the current passed by said pentode to said control winding, whereby the voltage across said load impedance is substantially independent of the alternating voltage in said control winding.

9. A control circuit comprising, a winding adapted to have alternating voltage thereon, a control tube having cathode, anode, and control grid means, an operating voltage source, a load impedance, said winding being connected to said anode, said operating voltage source being connected across the series combination of said winding, load impedance and control tube, said control tube having a characteristic throughout a portion of its operating range such that variations in anode-cathode voltage have substantially no affect on the anode-cathode current whereby the alternating voltage on said winding will not appear at the terminal thereof remote from said anode means, a utilization circuit, and means for connecting said utilization circuit between the control grid means and said remote terminal, to thus have substantially no alternating voltage from the alternating voltage on said winding appear in said utilization circuit,

References Cited in the tile of this patent UNITED STATES PATENTS 2,443,006 Iohnson June 8, 1948 2,513,983 Winn July 4, 1950 2,589,991 Clark Mar. 18, 1952 2,603,768 Trindle July 1S, 1952 

